Electric heating-pad.



C. WIRT.

ELECTRIC HEATING PAD.

APPLxcATloN FILED JuLYs, 1915.

Patented Aug. 20, 1918.

.1 L. J F n m n w L 1 u v Witnesses UNITED STATES PATENT OFFICE.

CHARLES WIRT, OF PHILADELPHIA, PENNSYLVANIA.

ELECTRIC HEATING-PAD.

Application led July 3, 1915.

To all whom t may concern:

Be it known that I, CHARLES lVin'r, a citizen of the United States, resident of Philadelphia, county of Philadelphia, State of Pennsylvania, have invented a certain 'new and useful ElectricHeating-Pad, of which the Afollowing is a specification.

The object I have in view is the constructionof an electric heating pad which will have the following desirable characteristics:

First.: It will be cheap to construct and durable in use.

Second: It will be flexible and Third: It will have the maximum radiation effect.

These and further objects will more fully appear from the following specification and accompanying drawings, considered together or separately, in which Figure l is a diagramma-tic view of a pad embodying my invention;

Fig. Q is a diagrammatic section thereof on ythe line X-X of Fig. l;

Fig. 3 is a similar` section of a modification; and

Fig. l is a similar View of another modification.

In all of the views, like parts are designated by similar reference characters.

One way of carrying out m-y invention is shown in Figs. l and 2. A refiexed conductor l extends back and forth on a supporting sheet'or base 2. Preferably it is reflexed in parallel rows. It is secured thereto by means of threads 3 arranged in rows of stitches. Any form of conductor may be employed and it may be of any cross section, but I prefer to make it of wire of small cross section. Preferably the wire is made of pure iron because it has a very high temperature variation, o., the resistance of the wire increases with the temperature, thus choking the current.

Any form of base sheet 2 may be einployed, but I prefer to use something that is fireproof, possesses insulating qualities and is iexible. Suitable materials for this purpose may be asbestos or mica. The threads 3 may be made of any filamentous substance, either reproof or not. As an example of suitableireproof material, asbestos thread may be employed. An example of non-fireproof material may be cotton or linen. Each stitch is formed of one, two or more threads, as de ends upon the character of the sewing machine employed. The threads are ar- Specication of Letters Patent.

latentedAug. 20, 1918.

Serial No. 37,817.

ranged at an angle to the conductor. Preferably this 1s a right angle as shown. Preferably each stitch or thread goes through both supporting sheets and over each section of the conductor and so on. )ne way of manufacturing the device is to use a sewing machine with multiple needles or needles arranged in gangs so that a plurality of par-4 allel rows of stitches may be made at one time. The needles will advance stitch by stitch as the conductor is drawn back and fort-h ac'rossthe sheets. The conductor is put against thel needles when the latter are in-their lowered position. The needles will thenrise and the sheets will advance one step'. The needles will then descend so as to make la loop over thetop of the sheet, thus holding they two sheets and the conductor firmly in place. As the gangs of needles extend over the length of the sheets in the direction of the length of the loops of the conductor, the latter will be stitched to the sheets in parallel lines. y

Fig. 3 shows another embodiment ofthe invention in which there are two sheets 2, 2 made of ireproof material, one sheet being on each side of the conductor.

Fig. 4 shows a further modification in which two additional sheets 5, 5 of non-fireproof material are employed which sheetsare outside of the fireproof sheets 2. 2. As examples of such material cotton or linen may be employed. Preferably a fabric is chosen formed of vegetable fibers. in contradistinction from animal fibers. The former will permit the readv escape of heat, the latter will not. I consider it desirable for the heat to beallowed to escape rather than to be retained.

Thethreads 8 may pass through all of the sheets and will bind them together aswell as securing the conductor in place. This structure is particularly applicable for heating pads for beds. in which moderate heat is necessary. In this construction the thread may be of cotton or linen. The heating wire being in Contact with the fireproof sheets only` the sheet 4, (or sheets 5, 5) not. being fireproof, therefore serves to inclose and support and to add flexibility and weight to the reproof sheets. An advantage of this latter construction is that it provides an arrangement whereby a certain quantity of heat can be dissipated by a certain surface. An ideal condition would be a flexible electric conductor. for example a'. graphite Ii'paint, covering the entire surface. This is 'not practical and to approximate this condition and secure a construction adapted to practical manufacture and use, I employ an electrical conductor so disposed as to cover a large percentage of the area of the sheet. It follows that the conductor itself must be at a higher temperature than the temperature of the exterior surface as a Whole. Therefore, when making the exterior surface of a flexible and durable fabric which is not ireproof and lining this, where it is in contact with the heating conductor, with a lreproof material, a structure is thereby made which as a Whole is well adapted to operate safely and with the minimum risk of danger on account of the inflammable nature of the surroundings. It is apparent that the direction of the flow vof heat will be away from the hot conductor to the cooler area of the surface. By employing the lirepr'oof sheets 2, 2, the immediate contact with the heated conductor and the inflammable exterior sheets 5, 5 is prevented. Materials such as asbestos, althou h classed as non-conductors of heat, are 1n fact fairly good heat conductors and will therefore serve to equalize the temperature in a structure of this kind. There will be to a great extent -a decrease in the possibility of scorching or Carbonizing the inflammable material as compared with an equivalent construction Where the fireproof lining is absent. To get the best results from the device, the distance between the parallel lines of the conductor should not be great, as otherwise the How of heat between adjacent portions of the conductor will not be suilicient to practically equalize the temperature. In' other words there will be lines comprising the valleys between the conductors which will not be elfective for heat radiation and there will be lines comprising the ridges where the temperature will be greater than desired.

It will be understood that the drawings are entirely diagrammatic as to proportion and as to the stitching. The diameter of the wire conductor is greatly exaggerated. As a matter of fact the conductor is preferably an extremly fine wire of high resistance material, Vand the distance between the wires will be approximately equal to the thickness of the threads, and the presence of the wire Will not detract from the flexibility of the pad as a whole.

In accordance with the provisions of the patent statutes, I have described the principle of my invention, together with the apparatus which I now consider to represent they best embodiment thereof; but I desire to have it understood that the apparatus shown is merely illustrative and that the ,invention may be carried outl in other ways.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. A heating pad composed of two flexible asbestos sheets, and a reflexed conductor formed of a material capable of high temperature Variations interposed between the sheets, and an outside covering of a material possessing strength and flexibility, the said sheets and covering beingsecured together and to the conductor in such a manner as to prevent movement of the conductor.

.2. A heating pad comprising a relexed metallic conductor, two sheets of asbestos on opposite sides of the conductor, an outside eovering of strong flexible non-fireproof material, and a plurality of rows of threads connecting the said sheets, covering and conductor together in such a manner as to prevent movement of the conductor, the convolutions of the conductor being separated one from the other by the thickness of the stitching only.

3. A heating ad comprising a reflexed bare-metallic conductor arranged in parallel rows, a sheet on each side of -said conductor formed of flexible asbestos, an outside sheet of flexible non-reproof material on each side and a plurality of rows of threads connectlng all the sheets together and tothe conductor in such a manner as to prevent movement of the conductor.

This specification signed and witnessed this second day of July, 1915.

ANNA E. BENTON, CHARLES SCHNEIDER. 

